Improved and more sensitive techniques for detecting the range of HIV-induced neurocognitive impairment (NCI) [asymptomatic neurocognitive impairment (ANI), mild neurocognitive disorder (MND) or HIV-associated dementia (HAD)] document NCI as a major co-morbidity of HIV-1 (HIV) infection. Building on the confluence of new information showing that CD14-positive Monocyte-associated HIV DNA Viral Load (CD14MADVL) correlates with NCI, coupled to unpublished data from co-investigator S. Gartner documenting a highly distinct virus in CD14 positive monocyte, the current proposal targets in depth pathogenesis research of the virus in this compartment drawing from a unique prospective cohort of treatment naive patients recruited from a large Nigerian PEPFAR program. The conceptual framework for this project draws from the well established fact that HIV enters the brain primarily via the trafficking of infected blood monocytes and virus in this compartment provides a window for understanding the pathogenesis of NCI without direct access to brain tissue. Our preliminary studies document capacity to enroll and detect large numbers of treatment naive patients with NCI, maintain them in prospective follow up and perform in depth laboratory analysis of the virus from monocytes, CD-14 negative mononuclear cells, plasma and CSF. The central hypothesis of this grant application is that the previously reported correlation between severity of NCI and CD14MADVL is linked to a distinctive pattern of viral quasi-species in this compartment (unpublished preliminary data) and that detailed analysis of viral motifs among the quasi-species from this compartment compared to non-monocyte HIV DNA and plasma viral RNA offer promise for identifying signature patterns that will inform NCI pathogenesis. This hypothesis will be addressed in two aims: Aim 1 - Classification of NCI and correlation with CD14MADVL in cross sectional study and longitudinally, and Aim 2 - Detailed study of the virus engaging targeted quasi-species analysis to characterize distinguishing motifs associated with NCI, and to study the relationship to viral subtype and the relationship of viral drug resistance in different compartments to NCI. The research team is comprised of internationally recognized HIV, neuro-AIDS and molecular virology experts from the University of Maryland, leading neuro-AIDS scientists from the University of California San Diego HIV Neurobehavioral Research Center (UCSD/HNRC), and local research investigators from the Institute of Human Virology-Nigeria (IHV-N) and affiliates in Nigeria. Additionally an extensive repository of viable peripheral blood cells, DNA and plasma will be collected for future studies.